Device-dependent selection between modes for asymmetric serial protocols

ABSTRACT

A portable communication device (PCD) can automatically switch into different operating modes of an asymmetric communication protocol (such as USB) depending on the type of accessory connected. For example, the accessory can signal whether the PCD should operate in a first mode or a second mode using a hardware indicator such as identification resistor across two pins of a multi-pin connector and/or a software indicator such as a command protocol. The PCD can detect the accessory&#39;s signal and switch to the operating mode requested by the accessory.

BACKGROUND

The present disclosure relates generally to portable communicationdevices that communicate with accessory devices using serial protocolsand in particular to device-dependent selection by the portablecommunication device between modes (or roles) of an asymmetric serialprotocol.

In recent years, a number of portable communication devices (PCDs) havebeen developed. Examples of PCDs include, for example, portable mediaplayers, mobile phones, personal digital assistants (PDAs), portablee-mail devices, video game players, portable navigation units relying onGlobal Positioning System (GPS) satellite data, and multi-functiondevices that can integrate numerous functions such as media storage andplayback, mobile phone, Internet access, e-mail, personal informationmanagement, game play, GPS/navigation capability, and the like. Examplesof multi-function PCDs include various iPhone® and iPod® modelsmanufactured and sold by Apple Inc., assignee of the presentapplication, as well as other portable electronic devices made and soldby other manufactures and distributors under their respective brandnames.

PCDs are frequently docked with other electronic devices, referred toherein as “accessories.” For example, from time to time, a user may docka PCD with a personal computer to synchronize media content and/ormetadata, personal data, and the like. A user may at other times dockthe same PCD with other electronic devices, such as an in-vehicle mediasystem, a speaker dock, or the like. The user may also dock the PCD witha charger that provides power to the PCD but does not include other dataor information sharing capability.

To facilitate communication between PCDs and accessories, it is commonto rely on standard point-to-point communication protocols, such asUniversal Serial Bus (USB). The USB specification (promulgated by USBImplementers Forum, Inc. and available at their website, www.usb.org)specifies two signal contacts, referred to as D+ and D−, for datatransmission and two additional contacts for power, referred to asV_(BUS) and specified as 5.0 volts (V), and ground. In a USB connection,a “USB host” delivers power to the V_(BUS) contact while a “USB device”relies on the USB host to provide the V_(BUS) power.

BRIEF SUMMARY

USB is an asymmetric communication protocol, in the sense that the USBhost and USB device use the connection contacts differently. This cancreate problems when connecting a PCD to different accessories atdifferent times, as some accessories may prefer the PCD to act as USBhost while other accessories prefer the PCD to act as a USB device. Forexample, when some PCDs connect to a computer via USB, the computer actsas USB host and provides power that can be used to charge the PCD.However, if a PCD connects to another portable electronic apparatus,such as a digital camera, the other apparatus may expect that it will beable to act as the USB device, in which case the PCD would need to actas a USB host. If the PCD cannot switch to a USB host mode, its abilityto connect to different accessories may be limited.

Certain embodiments of the present invention provide PCDs that canautomatically switch into one or another mode of an asymmetriccommunication protocol depending on the type of accessory connected. Insome embodiments, the accessory (which can be any electronic apparatusthat connects to a PCD) can signal its preference for whether the PCDshould operate in a first mode or a second mode of the asymmetricprotocol. Such signaling can be achieved, e.g., using a hardwaremechanism such as an identification resistor or a software mechanismsuch as a command protocol. The PCD can detect this preference andconfigure itself in the operating mode identified by the accessory.Thus, for example, if the asymmetric communication protocol is a USBprotocol, the accessory can indicate whether the PCD should operate as aUSB host or a USB device.

In some embodiments, the PCD can conform precisely to a standardprotocol such as USB when operating in one mode (e.g., USB device mode)but deviate from that protocol when operating in another mode (e.g., USBhost mode). For example, in accordance with standard USB protocols, theUSB host supplies 5.0 V of power on a V_(BUS) line to the USB device. APCD can receive 5.0 V of power when operating as a USB device but supplya lower voltage (e.g., 3.3 V) when operating as a USB host. This canreduce power consumption by the PCD.

The following detailed description together with the accompanyingdrawings will provide a better understanding of the nature andadvantages of the present invention.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates a PCD docked with a computer according to anembodiment of the present invention.

FIG. 2 illustrates a PCD docked with a sound system according to anembodiment of the present invention.

FIG. 3 illustrates a PCD docked with a digital camera according to anembodiment of the present invention.

FIG. 4 is a block diagram of a system according to an embodiment of thepresent invention.

FIG. 5 is a simplified connection diagram illustrating connections thatcan be provided between an accessory and a PCD according to anembodiment of the present invention.

FIG. 6 is a flow diagram of a process for establishing a connection toan accessory according to an embodiment of the present invention.

DETAILED DESCRIPTION

Certain embodiments of the present invention provide PCDs that canautomatically switch into one or another mode of an asymmetriccommunication protocol depending on the type of accessory connected. Insome embodiments, the accessory (which can be any electronic apparatusthat connects to a PCD) can signal its preference for whether the PCDshould operate in a first mode or a second mode of the asymmetricprotocol. Such signaling can be achieved, e.g., using a hardwaremechanism such as an identification resistor or a software mechanismsuch as a command protocol. The PCD can detect this preference andconfigure itself in the operating mode identified by the accessory.Thus, for example, if the asymmetric communication protocol is a USBprotocol, the accessory can indicate whether the PCD should operate as aUSB host or a USB device.

FIGS. 1-3 illustrate a PCD docked (or connected) to accessoriesaccording to embodiments of the present invention. In FIG. 1, PCD 102 isdocked with computer 104 via cable 106. Cable 106 in this embodiment caninclude wires to carry the standard USB signals (D+, D−, V_(BUS), andground) and can also include other wires. In one embodiment, connector108 connects cable 106 to a mating receptacle (not explicitly shown) ona bottom surface of PCD 102. The mating receptacle of PCD 102 mayinclude a larger number of pins than is required for USB communication(e.g., 30 pins in one embodiment), as described below with reference toFIG. 4. The additional pins can increase the range of accessories withwhich PCD 102 can be docked and the types of information that PCD 102can exchange with an accessory when docked. In one embodiment, connector110 connects cable 106 to a mating receptacle (not explicitly shown) ona side surface of computer 104. Connector 110 can be, for example, astandard USB connector, and the mating receptacle can be a standard USBreceptacle. In the configuration of FIG. 1, computer 104 can act as aUSB host while PCD 102 acts as a USB device.

In FIG. 2, PCD 102 is docked with sound system 204. Docking can beaccomplished by providing docking connector 206 (shown in inset 208) ona top surface of sound system 204 and inserting docking connector 206into the mating receptacle (not explicitly shown) of PCD 102. In thisconfiguration, docking connector 206 may include mating pinscorresponding to some or all of the pins in the mating receptacle of PCD102. Depending on the implementation of sound system 204, it may bedesirable for PCD 102 to present a USB host configuration or a USBdevice configuration.

In FIG. 3, PCD 102 is docked with digital camera 304 via cable 306. Insome embodiments, cable 306 can be similar to cable 106 of FIG. 1.Connector 308 connects cable 306 to a mating receptacle (not explicitlyshown) of PCD 102. Digital camera 304 can provide a USB receptacle or areceptacle with additional pins to receive a connector (not shown) atone end of cable 306. In some embodiments, digital camera 304 can onlyoperate as a USB device, in which case it is desirable for PCD 102 topresent a USB host configuration.

It will be appreciated that the PCD/accessory connections describedherein are illustrative and that variations and modifications arepossible. A PCD can connect to a wide range of other electronicapparatus, and the term “accessory” as used herein refers generally toany electronic apparatus with which a PCD can be connected. A PCD canoperate in either a USB host or USB device mode when connected to aUSB-compliant accessory. As described below, the operating mode that aPCD presents to an accessory can be controlled using accessoryidentification pins provided on the mating receptacle of PCD 102 andcorresponding pins on cable connector 106 or docking connector 206.

FIG. 4 is a block diagram of a system 400 according to an embodiment ofthe present invention. System 400 can include PCD 402 (e.g.,implementing PCD 102 of FIGS. 1-3) and an accessory 420 (e.g.,implementing any one of accessories 104, 204, 304 of FIGS. 1-3).

PCD 402 in this embodiment can provide communication and/or mediaplayback capability. PCD 402 can include processor 404, storage device406, user interface 408, power control module 410, battery 412, andaccessory input/output (I/O) interface 414. PCD 402 can also includeother components (not explicitly shown) to provide various enhancedcapabilities. For example, in some embodiments PCD 402 can include radiofrequency (RF) transceiver components for accessing wireless voiceand/or data networks (e.g., using cellular telephone technology,advanced data network technology such as 3G or EDGE, WiFi (IEEE 802.11family standards), or other mobile communication technologies, or anycombination thereof), a GPS receiver, and/or other components.

Storage device 406 can be implemented, e.g., using disk, flash memory,or any other non-volatile storage medium. In some embodiments, storagedevice 406 can store media assets such as audio, video, still images, orthe like, that can be played by PCD 402. Storage device 406 can alsostore other information such as a user's contacts (names, addresses,phone numbers, etc.); scheduled appointments and events; notes; and/orother personal information. In some embodiments, storage device 406 canstore one or more application programs to be executed by processor 404(e.g., video game programs, personal information management programs,etc.).

User interface 408 may include input devices such as a touch pad, touchscreen, scroll wheel, click wheel, dial, button, switch, keypad,microphone, or the like, as well as output devices such as video screen,indicator lights, speakers, headphone jacks, or the like, together withsupporting electronics (e.g., digital-to-analog or analog-to-digitalconverters, signal processors, or the like). A user can operate inputdevices of user interface 408 to invoke the functionality of PCD 402 andcan view and/or hear output from PCD 402 via output devices of userinterface 408.

Processor 404, which can be implemented as one or more integratedcircuits (e.g., a conventional microprocessor or microcontroller), cancontrol the operation of PCD 402. In various embodiments, processor 404can execute a variety of programs in response to program code and canmaintain multiple concurrently executing programs or processes. At anygiven time, some or all of the program code to be executed can beresident in processor 404 and/or in storage media such as storage device406.

Through suitable programming, processor 404 can provide variousfunctionality for PCD 402. For example, in response to user inputsignals provided by user interface 408, processor 404 can operate adatabase engine to navigate a database of media assets stored in storagedevice 406 in response to user input and display lists of selectedassets. Processor 404 can respond to user selection of an asset (orassets) to be played by transferring asset information to a playbackengine also operated by processor 404, thus allowing media content to beplayed. Processor 404 can also operate other programs to control otherfunctions of PCD 402.

Power control module 410 provides power management capability for PCD402. For example, power control module 410 can deliver power frombattery 412 to accessory I/O interface 414 via line 411 and to othercomponents of PCD 402 (connections not shown). Power control module 410can also receive power via accessory I/O interface 414 and line 413 anddeliver received power to various components of PCD 402 (connections notshown); received power can also be delivered to battery 412, therebyallowing battery 412 to be recharged via accessory I/O interface 414. Insome embodiments, power control module 410 can be implemented usingprogrammable or controllable circuits operating in response to controlsignals generated by program code executing on processor 404 or as aseparate microprocessor or microcontroller.

In some embodiments, power control module 410 is responsive to signalsfrom sensor 416 in accessory I/O interface 414. As described below,sensor 416 can generate a signal indicative of the type of accessoryconnected, and power control module 410 can use this information todetermine, e.g., whether to distribute power from battery 412 orreceived power from the accessory. Power control module 410 can alsoprovide other power management capabilities, such as regulating powerconsumption of other components of PCD 402 based on the source andamount of available power, monitoring stored power in battery 412 andgenerating user alerts if the stored power drops below a minimum level,and so on.

Accessory I/O interface 414 can allow PCD 402 to communicate withvarious accessories. For example, accessory I/O interface 414 mightsupport connections to a computer (e.g., as shown in FIG. 1), anexternal speaker dock (e.g., as shown in FIG. 2), a digital camera(e.g., as shown in FIG. 3), a radio tuner (e.g., FM, AM and/orsatellite), an in-vehicle entertainment system, an external videodevice, or the like. In accordance with some embodiments of theinvention, accessory I/O interface 414 can determine whether to operatein USB host or USB device mode when connected to an accessory. Asdescribed below, sensor 416 can be used to detect identifyinginformation from a connected accessory, and this identifying informationcan be used to select an operating mode.

In some embodiments, accessory I/O interface 414 can include aconnector, such as a 30-pin connector corresponding to the connectorused on iPod® and iPhone® products, as well as supporting circuitry. Theconnector can provide connections for power and ground as well as forvarious wired communication interfaces such as USB, FireWire, and/oruniversal asynchronous receiver/transmitter (UART). Thus, accessory I/Ointerface 414 can support multiple communication channels, and a givenaccessory can use any or all of these channels.

Accessory 420 includes controller 424, user interface 422, and PCD I/Ointerface 426. Accessory 420 is representative of a broad range ofelectronic apparatus to which PCD 402 can be connected, and it isunderstood that accessories can vary widely in capability, complexityand form factor. Various accessories may include components not shown inFIG. 4, including but not limited to storage devices (disk, memory,etc.); video screens, speakers, or ports for connecting to externalaudio/video devices; camera components such as lenses, image sensors,and controls for same (e.g., aperture, zoom, exposure time, frame rate,etc.); microphones for recording audio (either alone or in connectionwith video recording); and so on.

Controller 424 can include, e.g., a microprocessor or microcontrollerexecuting program code to perform various functions associated withaccessory 420. For example, where accessory 420 is a personal computersystem (e.g., as shown in FIG. 1), the program code can include anoperating system, a driver program associated with a USB port, and acontent management program that allows a user to control what content isstored on PCD 402 by interacting with user interface 422 of accessory420. In the case of a personal computer, program code executed bycontroller 424 can also include various application programs completelyunrelated to PCD 402. In some embodiments where accessory 420 is a soundsystem (e.g., as shown in FIG. 2), program code executed by controller424 can include programs for digital audio decoding, analog or digitalaudio processing, and the like. In some embodiments where accessory 420is a digital camera (e.g., as shown in FIG. 3), program code executed bycontroller 424 can include programs that allow a user to control thecamera to capture images, display images, transfer image data to anotherelectronic apparatus, etc.

User interface 422 may include input controls such as a touch pad, touchscreen, scroll wheel, click wheel, dial, button, switch, keypad,microphone, or the like, as well as output devices such as video screen,indicator lights, speakers, headphone jacks or the like, together withsupporting electronics (e.g., digital-to-analog or analog-to-digitalconverters, signal processors or the like). A user can operate thevarious input controls of user interface 422 to invoke the functionalityof accessory 420 and can view and/or hear output from accessory 420 viauser interface 422.

PCD I/O interface 426 can allow accessory 420 to communicate with PCD402 (or another PCD). In accordance with some embodiments of theinvention, PCD I/O interface 426 can incorporate a USB interface. Forexample, PCD I/O interface 426 can provide a standard, mini, or microUSB port. In other embodiments, PCD I/O interface 426 can include aconnector that mates directly with a connector included in PCD 402, suchas a 30-pin connector that mates with the connector used on variousiPod® products. Such a connector can be used to supply power to PCD 202or receive power from PCD 202, to receive audio and/or video signals inanalog and/or digital formats, and to communicate information viavarious interfaces such as USB, UART, and/or FireWire.

Accessory 420 can be any electronic apparatus that interacts with PCD402, including but not limited to any of the examples shown in FIGS.1-3. In some embodiments, accessory 420 can provide remote control overoperations of PCD 402, or a remote user interface that can include bothinput and output controls (e.g., a display screen). Accessory 420 invarious embodiments can control any function of PCD 402 and can alsoreceive media content from PCD 402 and present such content to the user(e.g., through audio speakers and/or video display screen, depending onthe type of media content). In other embodiments, PCD 402 can controloperations of accessory 420, such as retrieving image data from adigital camera incorporated into accessory 420, initiating an imagecapture operation, etc.

It will be appreciated that the system configurations and componentsdescribed herein are illustrative and that variations and modificationsare possible. The PCD and/or accessory may have other capabilities notspecifically described herein (e.g., mobile phone, global positioningsystem (GPS), broadband data communication, Internet connectivity,etc.).

Further, while the PCD and accessory are described herein with referenceto particular blocks, it is to be understood that these blocks aredefined for convenience of description and are not intended to imply aparticular physical arrangement of component parts. Further, the blocksneed not correspond to physically distinct components. Blocks can beconfigured to perform various operations, e.g., by programming aprocessor or providing appropriate control circuitry, and various blocksmight or might not be reconfigurable depending on how the initialconfiguration is obtained. Embodiments of the present invention can berealized in a variety of apparatus including electronic devicesimplemented using any combination of circuitry and software.

Accessory I/O interface 414 of PCD 402 and PCD I/O interface 426 ofaccessory 420 allow PCD 402 to be connected with accessory 420 andsubsequently disconnected from accessory 420. As used herein, PCD 402and accessory 420 are “connected” whenever a communication channel isopen between PCD I/O interface 426 and accessory I/O interface 414. Suchconnection can be achieved via direct physical connection, e.g., withmating connectors; indirect physical connection, e.g., via a cable;and/or wireless connection, e.g., via Bluetooth. PCD 402 and accessory420 are said to be “docked” whenever an electrical connection isestablished between pins of PCD I/O interface 426 and corresponding pinsof accessory I/O interface 414. Docking can be achieved directly, e.g.,with mating connectors, or indirectly, e.g., via a cable. In the case ofan indirect connection, the connectors for accessory 420 and PCD 402need not have corresponding form factors or numbers or arrangements ofpins.

In some embodiments, PCD 402 and accessory 420 can communicate whileconnected (e.g., docked) by exchanging commands and data according to aPCD-specific protocol. The commands and data can be communicated, e.g.,using USB Human Interface Device (HID) as a transport or using anothertransport provided by accessory I/O interface 414 and PCD I/O interface426. The PCD-specific protocol defines a format for messages to beexchanged between PCD 202 and accessory 220. For instance, thePCD-specific protocol may specify that each message (also referred toherein as a command) is sent in a packet with a header and an optionalpayload. The header provides basic information (e.g., a start indicator,length of the packet, and a command code identifying a command to beprocessed by the recipient), while the payload provides any dataassociated with the command; the amount of associated data can bedifferent for different commands, and some commands may provide forvariable-length payloads. In some embodiments, the commands may bedefined such that any particular command code is valid in only onedirection. The packet can also include error-detection orerror-correction codes as known in the art.

The accessory protocol can define a number of “lingoes,” where a “lingo”is a group of related commands that can be supported (or unsupported) byvarious classes of accessories. In one embodiment, a command code caninclude a first byte identifying the lingo to which the command belongsand a second byte identifying the particular command within the lingo.Other command structures may also be used. It is not required that allaccessories, or all PCDs to which an accessory can be connected, supportevery lingo defined within the accessory protocol.

In some embodiments, every accessory 420 and every PCD 402 that use thePCD-specific protocol support at least a “general” lingo that includescommands common to the PCD and all accessories. The general lingo caninclude commands enabling the PCD and the accessory to identify andauthenticate themselves to each other and to provide general informationabout their respective capabilities, including which (if any) otherlingoes each supports. The general lingo can also include authenticationcommands that the PCD can use to verify the purported identity andcapabilities of the accessory (or vice versa), and the accessory (orPCD) may be blocked from invoking certain (or all) commands or lingoesif the authentication is unsuccessful. In addition, in some embodimentsthe PCD can block the accessory from using USB functionality of the PCDif authentication is unsuccessful.

A PCD-specific protocol can also include various other lingoes, such asa simple remote lingo that allows accessory 420 to send a commandindicating a function of PCD 402 to be invoked, a remote user interfacelingo that can be used to communicate commands and data related toreplicating all or part of a user interface of PCD 402 on accessory 420(thereby supporting a more advanced remote control), a tuner lingo thatallows a user to control a tuner accessory 420 by operating PCD 402, astorage lingo that allows accessory 420 to store data on PCD 402, and soon. Any lingo or combination of lingoes or other commands or groups ofcommands can be used in connection with a PCD-specific protocol.

In some embodiment, the PCD-specific protocol can provide asoftware-based mechanism that allows an accessory to communicate adesired configuration for an asymmetric protocol to the PCD. Forexample, in the case where the asymmetric protocol is USB, the commandscan include a GetUSBMode command, a Return USBMode command and aSetUSBMode command. The GetUSBMode command can be sent by the accessoryto the PCD to request the current USB operating mode of the PCD. The PCDcan respond with the Return USBMode command, whose payload can include aparameter indicating the current USB mode (for example, USB host, USBdevice, or unconfigured). A SetUSBMode command can be sent by theaccessory to change the USB mode; the payload of this command caninclude a parameter indicating the desired USB mode. Other commands canalso be provided, and such commands can be part of a general lingo or aspecial-purpose lingo as desired.

In one embodiment using software mechanisms to control a USBconfiguration, the PCD and accessory can first connect using a transport(e.g., UART or a wireless transport) other than USB. The accessory canthen send commands of the PCD-specific protocol to determine the currentUSB mode of the PCD and/or to request that the PCD switch to the desiredmode.

In other embodiments, hardware mechanisms can be used to controlconfiguration of the asymmetric protocol. By way of illustration, FIG. 5is a simplified connection diagram illustrating connections that can beprovided between an accessory and a PCD according to an embodiment ofthe present invention. An accessory-side connector 502 is represented onthe left and a PCD-side connector 504 on the right. In some embodiments,accessory-side connector 502 can be part of PCD I/O interface 426 ofaccessory 402 of FIG. 4, and PCD-side connector 504 can be part ofaccessory I/O interface 414 of PCD 402 of FIG. 4. In other embodiments,features of accessory-side connector 502 can be incorporated, e.g., intoconnector 108 of FIG. 1, with only pins relevant to operation of theaccessory being connected to wires of cable 106.

In this example, PCD-side connector 504 provides a number of pins 510.(Herein, multiple instances of like objects are denoted with referencenumbers identifying the object and parenthetical numbers identifying theinstance where needed.) These pins include a number of ground (GND) pins510(1), 510(2), 510(8) and 510(10); USB D+ pin 510(2) and D− pin 510(3)for exchanging USB signals with the accessory; V_(BUS) pin 510(4) thatcan receive power (e.g., at 5.0 V) from an accessory; V_(P) pin 510(5)that can provide power (e.g., at 3.3 V) to an accessory; and accessoryidentification pins 510(6) and 510(7). Other pins, e.g., pin 510(9) canprovide signals not relevant to the present description, such as UARTsignals, FireWire signals, audio and/or video output signals to theaccessory in digital and/or analog formats, audio input signals from theaccessory, and so on. In one embodiment, PCD-side connector 504 can havea total of 30 pins; the number and arrangement of pins can be varied asdesired. In some embodiments, ground pins 510(1), 510(2), 510(8) and510(10) can be made longer than all other pins 510 so that the groundconnections are first to be made and last to be broken as PCD-sideconnector 504 engages with and disengages from accessory-side connector502. Such a configuration can reduce the risk of electrical damage to aPCD during docking and undocking.

Similarly, accessory-side connector 502 provides a number of pins 512.These pins include ground pins 512(1), 512(2), 512(8) and 512(10); USBD+ pin 512(2) and D− pin 512(3) for exchanging USB signals with theaccessory; V_(BUS) pin 512(4) that can provide power (e.g., at 5.0 V) toa PCD; V_(P) pin 512(5) that can receive power (e.g., at 3.3 V) from aPCD; and accessory identification pins 512(6) and 512(7). Other pins,e.g., pin 512(9) can provide signals not relevant to the presentdescription, such as UART signals, FireWire signals, audio and/or videoinput signals from the PCD in digital and/or analog formats, audiooutput signals to the PCD, and so on. In one embodiment, accessory-sideconnector 502 can have a total of 30 pins; the number and arrangement ofpins can be varied as desired.

As shown, PCD-side connector 504 and accessory-side connector 502provide the electrical connections required for a standard USBconnection (bidirectional D+ and D− signals, V_(BUS), and ground),although not necessarily in a form factor compliant with USB standards.Accessories that provide a USB port with a standard form factor can beconnected to PCD-side connector 504 using a cable (not shown in FIG. 5)that passes through the USB signals from accessory-side connector 502 toa standard USB connector (not shown). Any pins of accessory-sideconnector 502 that are not actually connected to the accessory can beleft floating or terminated to prevent line noise as appropriate, orunused signal contacts may simply be omitted.

FIG. 5 illustrates a technique that can be used in one embodiment toidentify whether the PCD should operate in a USB host or USB device modewhen connected to an accessory by using signals generated on accessoryidentification pins 510(6) and 510(7). Specifically, accessory-sideconnector 502 includes identification resistor 520 connected betweenpins 512(6) and 512(7). On PCD-side connector 504, pin 510(6) isconnected via a pull-up resistor 524 to a reference voltage (e.g.,V_(P), although a different voltage can also be used). Pin 510(7) isconnected to ground.

In operation, when accessory-side connector 502 is connected to PCD-sideconnector 504, electrical contact is achieved between pins 512(6) and510(6) and between pins 512(7) and 510(7). A voltage difference developsbetween nodes 526 and 528, and this difference is detected by sensor 530(e.g., implementing sensor 416 of FIG. 4). Since pull-up resistor 524 isfixed, the voltage difference corresponds to the resistance (R_(ID)) ofidentification resistor 520. Thus, sensor 530 can detect the resistanceR_(ID). In some embodiments, sensor 530 can output an analog or digitalsignal indicative of the resistance. In the embodiment of FIG. 4, thissignal can be delivered to power control module 410; the sensor signalcan also be delivered to processor 404 and/or other components of PCD402.

In one embodiment, different resistance values R_(ID) are associatedwith different USB operating modes of the PCD. For instance, a firstresistance value can indicate that the PCD should operate in a USB hostmode while a second resistance value can indicate that the PCD shouldoperate in a USB device mode. Certain embodiments may also use otherresistance values to provide other information. For example, the USBstandard defines various configurations that a USB device can present toa USB host, such as “human interface device” (HID) configuration or“mass storage device” configuration. Different resistance values R_(ID)can be associated with each of these USB device configurations.Accordingly, the same PCD can present a USB host mode to a firstaccessory, a USB device mode in an HID configuration to a secondaccessory, and a USB device mode in a mass storage configuration to athird accessory, depending on the resistance R_(ID) detected betweenpins 510(6) and 510(7) by sensor 530.

In some embodiments, some accessories can have connectors 502 that donot provide an identification resistor 520. For example, pins 512(6) and512(7) can be shorted together, or they can be disconnected from eachother. In such embodiments, the absence of resistor 520 can be detectedby sensor 530 and interpreted as a request for the PCD's “default” modeof operation. In one embodiment, the PCD operates in a mass-storage USBdevice mode by default and only switches to USB host mode if thespecific resistance R_(ID) associated with PCD-as-USB host configurationis detected.

It will be appreciated that the connector configuration described hereinis illustrative and that variations and modifications are possible.Different numbers and/or arrangements of pins can be substituted. Theconnector form factors may also vary. In the embodiment shown in FIG. 5,the PCD provides power on one pin when it is the USB host but receivespower on a different pin when it is the USB device. Differentaccessories can thus connect to one power pin or the other, depending onwhether the accessory is the USB device or the USB host, and do not needto (but may) connect to both. In other embodiments, the same pin can beoperated bidirectionally, with the PCD either receiving or supplying avoltage on that pin depending on whether it is the USB host or the USBdevice. Further, although in some embodiments, the power level isdifferent between PCD-as-USB host and PCD-as-USB device modes, this isalso not required. If the PCD as USB host does provide different power,any accessories operating as USB devices can be configured to accept thepower as provided. For example, an accessory may have a battery orconnect to an external power source if it requires more power than thePCD provides. Further, the PCD may use signal levels on the USB D+/D−lines that are limited to a maximum voltage level equal to the V_(P)line, and accessories can be configured to detect these voltage levels.

In some embodiments, the accessory can simply provide a standard USBinterface with a USB connection port having any standard form factor.The accessory may be fixedly configured to operate as either a USB hostor a USB device. For purposes of connecting the accessory to a PCDimplementing the identification scheme of FIG. 5, a cable such as cable106 of FIG. 1 or cable 306 of FIG. 3 can be configured with theappropriate resistor disposed within the PCD connector (e.g., connector108 of FIG. 1 or connector 308 of FIG. 3). If the accessory operates asa USB host, the V_(BUS) pin of connector 502 can be connected to the USBV_(BUS) pin. If the accessory operates as a USB device, the V_(P) pin ofconnector 502 can be connected to the USB V_(BUS) pin.

In some embodiments, an accessory can select or change itsidentification resistance R_(ID) to request different USB modes atdifferent times. For example, an accessory with which a PCD can dock mayprovide both a user input device (e.g., keyboard, mouse) or otherapparatus that presents as a USB device and a pass-through to a personalcomputer or other apparatus that presents as a USB host. Except when thePCD is actually in communication with the USB host, it can be instructedby the accessory to operate in USB host mode. In some embodiments, theaccessory can dynamically switch the resistance R_(ID) during operation.The PCD can monitor the identification pins, detect a change in R_(ID),and switch its USB mode accordingly.

Further, some accessories may be equipped with a standard USB On-the-Goreceptacle that includes an ID pin in addition to the four standard USBpins; the ID pin indicates to the USB On-the-Go accessory whether itshould operate as a USB host or USB device. For coupling a PCD to suchan accessory, a special role-selecting adapter can be provided (e.g., asa cable or unitary connector). One end of the adapter can include aconnector that mates with the PCD and supplies a resistance R_(ID)across the appropriate pins to indicate which USB mode the PCD shouldoperate in. The other end of the adapter can include a connector thatmates with the USB On-the-Go receptacle of the accessory and ties the IDpin to indicate that the accessory should operate in the other USB mode.Thus, for example, if R_(ID) at one end of the adapter indicates thatthe PCD should operate as USB host, the USB On-the-Go ID pin at theother end would indicate that the accessory should operate as USBdevice.

FIG. 6 is a flow diagram of a process 600 for establishing a connectionto an accessory according to an embodiment of the present invention.Process 600 can be implemented, e.g., in program code executing onprocessor 404 of PCD 402 (FIG. 4), in dedicated control logic withinaccessory I/O interface 414, or in any combination thereof.

Process 600 starts (block 602) when accessory I/O 414 interface detectsthat contact has been established between its connector pins (e.g., pins510 of connector 504 in FIG. 5) and corresponding pins of an accessoryconnector (e.g., pins 512 of connector 502). At block 604, sensor 530can sense the resistance R_(ID) across accessory identification pins510(6) and 510(7).

At block 606, it is determined whether the sensed resistance R_(ID)corresponds to the resistance associated with a request for the USB hostmode of the PCD. If so, then the PCD enters the USB host mode. If not,then at block 607, it is determined whether a host mode command (e.g., aSetUSBMode command requesting USB host mode) has been received from theaccessory. If the USB connection is not currently configured such thatthe accessory can use it to send PCD-specific protocol commands, anothertransport that has been configured (e.g., UART or a wireless transport)can be used for the command. If a host mode command is received at block607, the PCD can enter the USB host mode even if no resistance R_(ID) ora resistance R_(ID) not associated with host mode was sensed at block606.

Thus, the PCD can entersUSB host mode either in response to sensing theappropriate resistance R_(ID) at block 606 or receiving a commandrequesting host mode at block 607. Entering host mode can includevarious actions. For example, at block 608, the PCD can provide power tothe accessory, e.g., via V_(P) pin 510(5). The power provided to theaccessory can be the same as or different from standard USB powerlevels, as described above. At block 610, the PCD can receiveenumeration data from the accessory (which is operating in USB devicemode) via D+/D− pins 510(2), 510(3). Enumeration can be implementedaccording to USB standards, with the accessory providing variousidentifiers such as a vendor identifier and a model identifier. In someembodiments, the enumeration data can also include data specific tointeraction with the PCD, such as whether the accessory supportscommunication using a PCD-specific protocol via the USB connection.

On the other hand, if block 606 results in a determination that thesensed resistance R_(ID) does not correspond to the resistanceassociated with a request for the USB host mode of the PCD and block 607results in a determination that no command requesting USB host mode hasbeen received, then the PCD can enter a USB device mode. For example, atblock 612, the PCD can receive USB power (e.g., 5 V) from the accessory,e.g., via V_(BUS) pin 510(4). At block 614, the PCD can provideenumeration data to the accessory (which is acting as a USB host) viaD+/D− pins 510(2), 510(3). Similarly to the case where the PCD is actingas USB host, enumeration can be implemented according to USB standards,in this case with the PCD providing various identifiers such as a vendoridentifier and a model identifier.

After enumeration completes, the PCD and accessory can begin to exchangesignals via the USB D+ and D− pins, regardless of which of the two isthe USB host. Thus, for example, the PCD can provide USB digital audioto the accessory, or the accessory can transfer various data files to orfrom the PCD, or the like.

In some embodiments, the PCD can control the availability of USBfunctionality after enumeration. For example, at block 620, regardlessof whether the PCD or accessory acts as USB host, the PCD can determinewhether the accessory supports communication using a PCD-specificprotocol via the USB port or in some instances another port. If thePCD-specific protocol is not supported, then process 600 can exit (block622). In some embodiments, the PCD can permit the accessory to use atleast some USB functionality even if the PCD-specific protocol is notsupported; in other embodiments, the PCD locks out further USBcommunication with any accessory that does not support the PCD-specificprotocol.

If the PCD-specific protocol is supported, then at block 624, the PCDcan receive identification data from the accessory. This data caninclude, e.g., a list of which lingoes of the PCD-specific protocol aresupported by the accessory, information as to the accessory'spreferences for initial configuration (such as whether various inputsand/or outputs should be enabled or disabled), and so on. In someembodiments, the identification data can be sent by the accessory usingone or more commands of a general lingo of a PCD-specific protocol viathe USB transport link that has been established.

At block 626, the PCD can initiate an authentication process with theaccessory. In some embodiments, the authentication operation can includeverifying a digital certificate provided by the accessory and testing acryptological digital signature provided by the accessory against apublic key associated with the digital certificate. In some embodiments,authentication operations may be facilitated using an authenticationcontroller that can be embedded into PCD I/O interface 432 of accessory420 as shown in FIG. 4. In other embodiments, an authenticationcontroller may be embedded in a cable connecting the accessory to thePCD, and authentication for the USB connection can be provided by acontroller that communicates using pins other than the USB pins.

At block 628, it is determined whether the authentication processsucceeded. If so, then at block 630, the PCD can unlock USBfunctionality for use by the accessory. For example, in someembodiments, the PCD can permit the accessory to enumerate and sendcertain commands of the PCD-specific protocol via the USB port withoutfirst having successfully authenticated. Following block 630,communication can continue (block 636) until the connection isterminated. In some embodiments, an established USB connection can beused at block 636 to exchange commands of the PCD-specific protocol withUSB as the transport.

In some embodiments, communication at block 636 can include changing themode of the USB connection. In some embodiments, after initiallyestablishing a configuration for the USB connection, the accessory canchange the established configuration, e.g., by changing R_(ID) or bysending a SetUSBMode command. Depending on implementation, sending of aSetUSBMode command using USB as the transport might or might not besupported; if it is not, another transport (e.g., UART or wireless) canbe used.

If, at block 628, it is determined that the authentication processfailed, then at block 632, the PCD can notify the accessory of theauthentication failure, and process 600 can end (block 634). In thiscase, the PCD can block the accessory from accessing PCD functionalitysuch as commands of the PCD-specific protocol or USB functions such asfile access, digital audio transfer, or the like. Unauthorized USBfunctions can be blocked, e.g., by the PCD refusing to respond torequests from the accessory (or sending error messages in response tosuch requests) and/or by the PCD not initiating certain USB operationssuch as audio output. In some embodiments, the PCD can selectively blockor permit access to USB functionality regardless of whether it iscurrently operating in USB host or USB device mode.

It will be appreciated that the process described herein is illustrativeand that variations and modifications are possible. Steps described assequential may be executed in parallel, order of steps may be varied,and steps may be modified, combined, added or omitted. For example, insome embodiments, the accessory and PCD can initially establishcommunication using a transport other than USB (e.g., UART or a wirelesstransport) and can perform the authentication process of thePCD-specific protocol before configuring the USB connection. In someembodiments of this kind, the PCD can disregard accessory requests for aparticular USB configuration if the authentication fails.

Some embodiments may provide only hardware control of the USB mode(e.g., using an identification resistor), only software control (e.g.,using a mode-selection command of a PCD-specific protocol), or acombination of the two. For example, an identification resistor can beused to establish an initial configuration, which can later be changedby a mode-selection command. Alternatively, the PCD can disregard (ortreat as error) any received mode-selection command that conflicts witha mode selected based on an identification resistor.

In some embodiments, a PCD operating in USB host mode can supportmultiple concurrently connected USB devices. If, in such an arrangement,an accessory requests that the PCD switch to USB device mode while otherUSB devices are connected, the PCD can disregard the request and/orgenerate an error message to the requesting accessory.

Embodiments described herein thus provide flexible communication betweena PCD and a range of different accessories by allowing the PCD tooperate in either a USB host or USB device mode and allowing theaccessory to signal its preferred mode to the PCD.

While the invention has been described with respect to specificembodiments, one skilled in the art will recognize that numerousmodifications are possible. For example, a “PCD” refers generally to anyportable electronic device with any form of communication and/or mediaplayback capability; a broad range of functionality may be incorporated.Similarly, the term “accessory” includes any electronic device capableof docking or otherwise connecting with a PCD.

USB is used herein as an example of an asymmetric protocol, where theterm “asymmetric protocol” refers generally to a protocol for connectingtwo electronic devices in which each electronic device plays a distinctrole. In the context of USB, the roles are commonly known as “host” and“device,” and that terminology is used herein to distinguish twodifferent roles. However, it is understood that a variety of asymmetricprotocols exist and the roles can be identified under other nomenclature(such as “master” and “slave” or “A-type” and “B-type” or “first mode”and “second mode”). Techniques similar to those described herein can beapplied to any other asymmetric protocol, thus allowing a connected PCDto change its role on a per-connection basis. Accordingly, the presentinvention is not limited to the context of USB but can be used inconnection with any asymmetric protocol and any transport includingwired and/or wireless transports.

Embodiments of the present invention can be realized using anycombination of dedicated components and/or programmable processorsand/or other programmable devices. The various processes describedherein can be implemented on the same processor or different processorsin any combination. Accordingly, where components are described as beingconfigured to perform certain operations, such configuration can beaccomplished, e.g., by designing electronic circuits to perform theoperation, by programming programmable electronic circuits (such asmicroprocessors) to perform the operation, or any combination thereof.Processes can communicate using a variety of techniques including butnot limited to conventional techniques for interprocess communication,and different pairs of processes may use different techniques, or thesame pair of processes may use different techniques at different times.Further, while the embodiments described above may make reference tospecific hardware and software components, those skilled in the art willappreciate that different combinations of hardware and/or softwarecomponents may also be used and that particular operations described asbeing implemented in hardware might also be implemented in software orvice versa.

Computer programs incorporating various features of the presentinvention may be encoded on various computer readable storage media;suitable media include magnetic disk or tape, optical storage media suchas compact disk (CD) or DVD (digital versatile disk), flash memory, andthe like. Computer readable media encoded with the program code may bepackaged with a compatible electronic device, or the program code may beprovided separately from electronic devices (e.g., via Internetdownload).

Thus, although the invention has been described with respect to specificembodiments, it will be appreciated that the invention is intended tocover all modifications and equivalents within the scope of thefollowing claims.

What is claimed is:
 1. A method for use in a portable communicationdevice, the method comprising: establishing a connection to anaccessory; determining whether a mode-selecting signal is received fromthe accessory, the mode-selecting signal indicating whether the portablecommunication device is to operate in a first mode or a second mode ofan asymmetric communication protocol; in the event that themode-selecting signal is received from the accessory, operating theportable communication device in the mode indicated by themode-selecting signal; and in the event that the mode-selecting signalis not received from the accessory, operating the portable communicationdevice in the first mode of the asymmetric communication protocol. 2.The method of claim 1 wherein the connection to the accessory isestablished using a connector having a plurality of pins and whereindetermining whether the mode-selecting signal is received from theaccessory includes: sensing a resistance across two pins of theplurality of pins; and determining whether the sensed resistancesatisfies a first criterion, wherein the second mode is indicated in theevent that the sensed resistance satisfies the first criterion.
 3. Themethod of claim 2 wherein the two pins that are used for sensing theresistance are used exclusively for sensing the resistance.
 4. Themethod of claim 2 wherein the asymmetric communication protocol is aUniversal Serial Bus (USB) protocol, the first mode corresponds to adevice mode of the USB protocol, and the second mode corresponds to ahost mode of the USB protocol.
 5. The method of claim 4 furthercomprising: determining whether the sensed resistance satisfies a secondcriterion, wherein operating the portable communication device in afirst mode of the asymmetric communication protocol includes: operatingthe portable communication device in a Human Interface Deviceconfiguration of a device mode of the USB protocol in the event that thesensed resistance satisfies the second criterion; and operating theportable communication device in a mass storage configuration of thedevice mode of the USB protocol in the event that the sensed resistancedoes not satisfy the second criterion.
 6. The method of claim 1 whereinthe portable communication device further supports a device-specificprotocol, the method further comprising: initiating an authenticationoperation with the accessory according to the device-specific protocol;determining whether the authentication operation is successful; and inthe event that the authentication operation is not successful, blockingthe accessory from using at least one function associated with theasymmetric communication protocol.
 7. The method of claim 1 wherein theconnection to the accessory is established using a connector having aplurality of pins and wherein: operating the portable communicationdevice in the first mode includes receiving a first voltage level on afirst power pin of the plurality of pins, and operating the portablecommunication device in the second mode includes providing a secondvoltage level on a second power pin of the plurality of pins, whereinthe first voltage level is greater than the second voltage level.
 8. Themethod of claim 1 wherein determining whether a mode-selecting signal isreceived from the accessory includes determining whether amode-selecting command has been received from the accessory.
 9. Aportable communication device comprising: a processor; a power controlmodule coupled to the processor; and an accessory interface coupled tothe processor and the power control module, the accessory interfaceincluding: a connector having a plurality of pins, the plurality of pinsincluding a data pin associated with an asymmetric communicationprotocol, a power input pin coupled to the power control module, a poweroutput pin coupled to the power control module, and a pair of accessoryidentification pins; and a sensor connected to detect a resistanceapplied across the pair of accessory identification pins and configuredto generate an identification signal indicative of the detectedresistance, wherein the power control module is configured to determine,based on the identification signal, whether to provide a first power tothe power output pin or to receive a second power from the power inputpin; and wherein the accessory interface is configured to determine,based at least in part on the identification signal, whether to operatein a first mode or a second mode of the asymmetric communicationprotocol.
 10. The portable communication device of claim 9 wherein theasymmetric communication protocol is a USB protocol.
 11. The portablecommunication device of claim 9 wherein the power control module isfurther configured such that the first power and the second power are atdifferent voltage levels.
 12. The portable communication device of claim9 wherein the accessory interface is further configured to receive amode-selection command from the accessory and to determine whether tooperate in the first mode or the second mode of the asymmetriccommunication protocol based in part on the identification signal and inpart on the received mode-selection command.
 13. A portablecommunication device comprising: a processor; and an accessory interfacecoupled to the processor, the accessory interface being configured toselectively operate in a first mode or a second mode of an asymmetriccommunication protocol, the accessory interface being further configuredto receive a mode-selection command from the accessory and to determine,based at least in part on the mode-selection command, whether to operatein the first mode or the second mode of the asymmetric communicationprotocol.
 14. The portable communication device of claim 13 wherein theasymmetric communication protocol is a USB protocol.
 15. The portablecommunication device of claim 13 wherein the accessory interfaceincludes a connector having a plurality of pins, the plurality of pinsincluding a power input pin and a power output pin, the portablecommunication device further comprising: a power control module coupledto the power input pin and the power output pin, the power controlmodule being configured to receive power from the power input pin whenthe accessory interface is operating in the first mode of the asymmetriccommunication protocol and to provide power to the power output pin whenthe accessory interface is operating in the second mode of theasymmetric communication protocol.
 16. An accessory for use with aportable communication device, the accessory comprising: a controlleroperable in a device mode of a Universal Serial Bus (USB) protocol; aconnector coupled to the controller and adapted to connect to a portablecommunication device, the connector having a plurality of pins, theplurality of pins including a USB power pin, a USB ground pin, two USBdata pins, and a pair of accessory identification pins; and a resistorconnected between the accessory identification pins, wherein theresistor has a resistance value indicating to the portable communicationdevice that the portable communication device should operate in a hostmode of the USB protocol.
 17. The accessory of claim 16 wherein theplurality of pins further includes a power input pin to receive powerfrom the portable communication device.
 18. The accessory of claim 17wherein the power received from the portable communication device is ata lower voltage level than a standard USB voltage level.
 19. Theaccessory of claim 18 wherein the power received from the portablecommunication device is at a voltage level of approximately 3.3 volts.20. A method for use in an accessory, the method comprising:establishing a connection to a portable communication device, whereinthe portable communication device is switchable between a first mode anda second mode of an asymmetric communication protocol; sending a firstcommand to the portable communication device, the first commandspecifying a first requested mode of operation to be used by theportable media device, the first requested mode being one of the firstmode or the second mode, wherein in the event that the accessoryoperates in the first mode of the asymmetric communication protocol, therequested mode is the second mode, and wherein in the event that theaccessory operates in the second mode of the asymmetric communicationprotocol, the requested mode is the first mode; and communicating withthe portable media device using the asymmetric communication protocol.21. The method of claim 20 further comprising: prior to sending thefirst command, selecting the requested mode based at least in part on acurrent configuration of the accessory.
 22. The method of claim 20wherein the first command is sent using a transport that is independentof the asymmetric communication protocol.
 23. The method of claim 20further comprising: sending a second command to the portablecommunication device, the second command specifying a second requestedmode of operation to be used by the portable media device, the secondrequested mode being different from the first requested mode.
 24. Amethod for use in an accessory, the method comprising: establishing aconnection to a portable communication device using a connector having aplurality of pins, wherein the portable communication device isswitchable between a first mode and a second mode of an asymmetriccommunication protocol; applying a resistance across a first pin and asecond pin of the plurality of pins, wherein the resistance has a valueindicating to the portable communication device that the accessoryoperates in the first mode of the asymmetric communication protocol;receiving power from the portable communication device via a third pinof the plurality of pins; and communicating with the portablecommunication device using the first mode of the asymmetriccommunication protocol.
 25. The method of claim 24 wherein theasymmetric communication protocol is a Universal Serial Bus (USB)protocol and the first mode is a device mode of the USB protocol. 26.The method of claim 25 wherein receiving the power from the portablecommunication device includes receiving the power at a voltage levellower than a standard voltage level of the USB protocol.
 27. The methodof claim 25 wherein communicating with the portable communication deviceusing the first mode of the asymmetric communication protocol includessending USB-compliant enumeration data to the portable communicationdevice.
 28. The method of claim 27 further comprising, after sending theUSB-compliant enumeration data: sending a command to the portablecommunication device, wherein the command is one of a plurality ofcommands of a device-specific protocol supported by the portablecommunication device, wherein sending the command includes using theasymmetric communication protocol as a transport.